1. Field of the Invention
The present invention relates to apparatuses for coating paper and, more particularly, to such an apparatus for coating the web at the wet end of the papermachine.
2. Description of the Prior Art
Originally, practically all paper coating was carried out off-machine, that is as a completely separate operation which is not effected on the papermachine as opposed to on-machine coating which constitutes a step executed directly on the paper-machine. Such off-machine paper coating apparatuses obviously resulted in a costly operation requiring expensive equipment.
Later, on-machine coating proved feasible although it was performed on the web after the web had entered the dryer section and had been partially dried thereby. Probably the least costly on-machine coating method was based on size press coating performed on a papermachine having a size press located well within the dryer section. However, using such a size press for coating meant that water was being added to the web after most of the water had already been driven off by the dryer itself. Furthermore, the press itself limited the range of coating weights and materials. While a few wet end coating methods have been proposed, none have found commercial success as they did not perform well or were to costly.
Moreover, coating was generally reserved for paper products that could command a fairly high market price. Newsprint was not such a product. In addition, public demand that more recycled fibers be used in the manufacture of newsprint increased. In response, the publishers recently passed this demand onto the newsprint producers. Unfortunately, the use of recycled fibers tends to lead to increased linting. An inexpensive newsprint coating method would not only solve the linting problem but would also improve various paper properties as well as the overall quality of the printing. One such property would reside in opacity which in turn would allow for the use of less expensive fiber furnishes.